1. Field of the Invention
The present invention relates to an apparatus for processing a TV video signal, and more particularly, to a video signal format converting apparatus for doubling a horizontal/vertical frequency, and converting the composition ratio of a luminance signal to a color-difference signal, by which both horizontal/vertical frequency-converted and frequency-unconverted input signals can be processed.
2. Description of the Related Art
In a conventional digital TV signal processing method, flickering phenomenon or resolution is improved by converting a digital TV signal into a video signal whose vertical frequency is doubled by double scan conversion, or converting the digital TV signal into a video signal whose horizontal frequency is doubled by progressive scan conversion.
Three signals, luminance information Y and color-difference information U and V, are included in a pixel constituting a horizontal line (scanning line) of a TV screen or the like, and are represented by certain ratios according to the amount of information in the signals. That is, when the amount of color-difference information is not reduced, the three signals are represented by the ratio of 4:4:4. When the amount of color-difference information is halved in the horizontal direction, the three signals are represented by the ratio of 4:2:2. When the amount of color-difference information is reduced to one quarter in the horizontal direction, the three signals are indicated by the ratio of 4:1:1.
In particular, in the case of 4:4:4, the amount of data in each of the luminance signal and the color-difference signals is the same, and one luminance signal and two color-difference signals correspond to one pixel. Since, there is a larger amount of data in the ratio of 4:4:4 than in the other composition ratios, the quality of the image is increased.
As shown in FIG. 1, according to the prior art, a signal decoded by a decoder 101 has a composition ratio of 4:1:1 or 4:2:2. Thus, a horizontal/vertical frequency converter 102 is needed, which doubles the horizontal/vertical frequency of the decoded signal, using a progressive scan conversion method or a double scan conversion method.
Next, a format converter 103 converts the scanning-converted video signals having a composition ratio of 4:1:1 or 4:2:2 into signals having a composition ratio of 4:4:4 to improve the image quality of the video signals, and outputs the resultant signals to a multiplexer 104.
R, G, and B analog input signals are converted into digital Y, U, and V signals, having the composition ratio of 4:4:4, by an analog-to-digital (A/D) converter 105 and a space converter 106, and the digital Y, U, and V signals are output to the multiplexer 104.
Then, the multiplexer 104 selects and outputs the converted external input signals or an internally-processed signal according to a control selection signal.
According to the prior art as described above, external R, G, and B input signals received from a personal computer or the like are progressive scan converted or double scan converted. Only a signal having a doubled horizontal or vertical frequency can be processed, whereas signals whose horizontal or vertical frequency has not been doubled cannot be processed.